Electrodeposition of nickel

ABSTRACT

Known nickel plating baths can have large amounts of chloride incorporated in them. An improved nickel plating bath is described which has water-soluble bromide in it, preferably many times the weight of nickel present. The bath can include other electrodepositable metals besides nickel, so that the electrodeposition of hard nickel alloys can also be accomplished. The main result of the high bromide formulations proposed is to give deposits of nickel or its alloys which are notably free from stress. Many examples of nickel plating baths are given.

United States Patent Barrett 1 June 20, 1972 s41 ELECTRODEPOSITION 0F NICKEL FOREIGN PATENTS OR APPLICATIONS [72] inventor: Ernest Charles Henry Barrett, Th rn n 902,499 8/1962 Great Britain ....204/49 Heath, England 1,059,915 2/1967 Great Britain ..204/49 [73] Assignee: London & Scandinavian Metallurgical Co.,

Limited, London, England OTHER PUBLICATIONS [22] Filed: May 4, 1970 Endicott et all, Plating, Vol.43, No. l, p. 47 Jan. 1966 PP N05 ,638 Primary Examiner-F. C. Edmundson Attorney-McGlew and Toren [30] Foreign Application Priority Data [57] ABSTRACT May 7, 1969 Great Britain ..23,285/69 Known nickel plating baths can have large amounts of [52] chloride incorporated in them. An. improved nickel plating [51] bath is described which has water-soluble bromide in it, [58] preferably many times the weight of nickel present. The bath can include other electrodepositable metals besides nickel, so References Cited that the electrodeposition of hard nickel alloys can also be ac- UNXTED STATES PATENTS complished. The main resi lt of the high bromide formulations proposed 18 to give deposits of nickel or its alloys which are .2 1966 ph n on 8t 1-". notably free from stress. Many examples of nickel plating 3,271 ,274 9/1966 Guilio et al. ..204/43 baths are given 3,454.3 76 7/1969 Luce et al ..204/49 3,489,660 l/l970 Semienko et a]. ..204/43 9 Claims, No Drawings ELECTRODEPOSITION F NICKEL This invention relates to the electrodeposition of nickel and nickel-containing alloys and is particularly. concerned with providing an improved method of forming electrodeposits of nickel or of nickel alloys.

Nickel electroplating commonly uses, as the electrolytic bath. a solution of a nickel salt, e.g. nickel sulphate or sulphamate or nickel chloride, other components being included to produce a harder deposit or to reduce stress or to improve the performance of the electrolytic process. The production of a harder deposit normally involves the inclusion in the plating bath of a source of one or more metal ions in addition to nickel ions, so that more than one metal is plated out and the deposit is a nickel-based alloy. The reduction of stress and other improvements in the electrolytic process often involve the inclusion in the bath of components which do not plate out with the nickel, so that the deposit is nickel rather than a nickel alloy. Since essentially the same conditions apply to electroplating with nickel and to electroplating with nickel alloys, references to nickel plating herein are intended to refer generally to both nickel and nickel alloy deposits unless otherwise indicated.

It is known to include alkali metal chlorides in nickel plating baths. A considerable advance in nickel plating technique is described in British Patent specification No. 765,958, based upon the discovery that much larger amounts of sodium or potassium chloride than had previously been used gave improved throwing power and reduced stress. In an electrolytic bath according to British specification No. 765,958, the amount of sodium or potassium chloride is 7 to l2, and preferably 8, times the amount of nickel present in the nickel salt by weight.

lt has now been discovered that an increase in throwing power and greater reduction in the tensile stress of the resultant nickel deposit can be obtained by incorporating in a nickel plating bath a large amount of a soluble bromide.

It has previously been proposed to incorporate bromides in nickel plating baths. for the purpose of promoting anode corrosion and so increasing anode efficiency. The bromide is usually introduced as nickel bromide, as in the Harstan nickel sulphamate process. The amount of bromide used up till now has been relatively small, e. g. up to one-third of the amount of nickel present by weight.

The present invention is based upon the use, in an acid nickel electrolyte including a source of nickel ions, an amount of bromide ions in excess of the amount stoichiometrically equivalent to the amount of nickel ions calculated as nickel bromide.

According to one aspect of this invention, a nickel plating bath comprises an aqueous solution containing at least one water-soluble nickel salt as a source of nickel ions and at least one water-soluble bromide as a source of bromide ions, the amount of the bromide preferably being to times and most preferably l0 times the amount of nickel by weight. Stated otherwise, the amount of bromide ions present is greater than if the nickel ions are derived from nickel bromide as the sole source of nickel ions in the bath.

The invention also provides a method of forming a nickel or nickel alloy electrodeposit, which may be an electroform, which comprises electrolyzing a plating bath of the composition just defined. 7

The benefits of the present invention are obtained with any bromide which has the essential requirements of being watersoluble and of not containing any ions which might adversely affect the performance of the bath. For example, the invention can be carried out both with sodium bromide and with potassium bromide. Moreover, the other alkali metal bromides and ammonium bromide can be used. It is surprising that bromides are effective in the way now discovered, for it has been found that sodium and potassium iodides have no comparable effect to that of the corresponding bromides.

The electrodeposit or electroform formed with a plating bath according to this invention can either be nickel or a nickel-based alloy. The requisite source of nickel ions can, if

desired, be provided wholly or partly as nickel bromide, which also contributes to the source of bromide ions also needed, though in this case additional bromide ions must be provided. Any other water-soluble nickel compound can also provide the source of nickel ions, though for most practical baths it is constituted by nickel chloride.

The source of bromide ions is preferably provided by sodium bromide, which is the water-soluble bromide most readily available. The other alkali metal bromides, which are regarded as comprising those of potassium, ammonium, lithium, rubidium and caesium for the purposes of this invention are also eminently suitable, though the latter three are somewhat costly. More than one bromide can be provided in the same bath if desired.

The acidity of the plating bath is important and in practice the pH of the bath should not normally be above 5.0 and, for most purposes, not above 4.0. A preferred range of pH is 1.8-4.0, the most suitable pl-l usually being about 3.5; higher pHs up to 4.5 are suitable if the bath is formulated so as to produce an alloy deposit.

Other components of the bath besides the nickel and bromide ions can be incorporated in order to achieve a variety of different effects. Other electrodepositable metal ions which can be included are, for example, one or more of cobalt, iron, zinc, manganese, uranium, molybdenum and vanadium. The invention can be used for the electrodeposition of low-stress or even substantially stress-free nickel/cobalt, nickel/iron and other alloys.

Another advantageous feature of the invention consists in the optional inclusion in a nickel or nickel alloy bath of the invention of a small amount of sulphite ion, e.g. provided in the form of sodium sulphite. A suitable quantity is constituted by up to 0.6 g/l of sodium sulphite; larger concentrations are possible, but it is usually unnecessary to use them. The main benefit afforded is stress reduction in the resultant deposits; low stress, coupled with high throwing power and heat-resistance, are characteristic benefits of the invention; with the inclusion of sodium sulphite, the stress can be further reduced and it is possible to obtain deposits with virtually no stress or even with compressive stress.

Organic stress reducers, i.e. compounds which are known to have a reducing effect upon the stress in a deposit, may be incorporated in baths of the invention inorder to augment the tendency of the bathos to produce low-stress deposits or to ensure that stress is maintained sufficiently low. Suitable additives for this include saccharin, sodium naphthalene trisulphonate, sodium meta-benzene disulphonate and other conventional stress reducers.

The acid electrolyte of the invention serves to produce an evenly distributed nickel or alloy deposit over a wide current density range, without excessive over-growths; stated otherwise, the electrolyte has high throwing power.

Throwing power may be defined as the characteristic of a solution which determines the evenness with which a metal may be deposited from it. There are several methods of determining the throwing power of a solution, such as those based upon the Haring cell or the Field apparatus. The test used to determine the throwing power of the present invention is that which was used for the solution described in specification No. 765,958, namely: weighing the deposit per unit area at the extreme inside center of a angular test piece consisting of two square faces 2 X 2 inches at right angles to each other, stopped off at the back, dividing this weight by the weight per unit area deposited on the extreme outside corners and multiplying the result by 100.

The deposits obtained by electrolyzing a bath according to the invention without conventional stress reducers are heatresistant, for instance they are capable of being brazed. Heatresistant deposits have hitherto only been obtained from solutions which have a low inherent stress, such as nickel sulphamate baths. Such solutions usually have a low throwing power and consequently produce deposits which have very uneven distribution with nodular over-growths. The invention for the first time provides a bath capable of forming a nickel or nickel alloy deposit at high throwing power, the deposit being both heat-resistant and free from excessive stress.

A nickel deposit produced with a bath according to this invention typically has a Rockwell C hardness in the range of 20-30 Rc. Harder deposits can be obtained by modifying the bath composition and the conditions of operating and hardnesses of 50 Re or even higher can be achieved. One effect of the inclusion of other electrodepositable ions besides nickel ions in the bath is to produce a nickel alloy deposit which is often characterized by greater hardness. Of the alloying constituents mentioned above, cobalt, manganese, molybdenum and vanadium and mixtures thereof, in particular, when incorporated in the high bromide bath of the invention, preferably as the respective chlorides, give hard alloy deposits. For example, 5 g/l of cobalt gives hardnesses up to 480 DPN and 0.1-0.5 g/l of manganese gives hardnesses up to 350 DPN.

The deposits have a very low stress, which can often be obtained without the use of organic stress reducers, and can be produced at relatively high current densities, e.g. up to 100 A.S.F. The plating bath of the invention can be used without agitation or with agitation, such as air agitation, stirring or rod movement.

Unlike known nickel plating solutions, the solutions of this invention provide a combination of good hardness, ductility and low stress characteristic of nickel deposited without the use of organic stress reducers.

Further, it has been found that in the event of a failure of the source of current during electroplating, it is possible to continue plating without the occurrence of laminations simply by reversing the polarity for a short period and then recommencing plating.

Typical plating bath compositions of the invention are as follows:

Ni l-60 H BO 32 (25-40) Breg provided as NaBr or KBr) 100-600 pH 3.0-4.0 Operating temperature l850 C.

EXAMPLE 1 A bath was made up as an aqueous solution of the following composition:

Ni 30 Sodium bromide 300 Boric acid 32 Co (as cobalt chloride) The bath had a pH of 3,5 and was operated at 40 C. at a current density of up to 40 ASP. in still conditions and up to 80 ASP. with air or other agitation.

A fine-grained, hard, ductile and low-stress deposit of nickel alloyed with cobalt was obtained.

5 out in the table.

EXAMPLE 2 Nickel chloride l22 Boric acid 32 Ammonium bromide 200 EXAMPLE 3 Nickel sulphate 144 Boric acid 32 Sodium bromide 200 Sodium sulphite 0.5

EXAMPLE 4 Nickel chloride l22 Boric acid 32 Sodium bromide 200 Uranyl acetate 0.04

EXAMPLE 5 Nickel sulphate I44 Boric acid 32 Sodium bromide 200 Ferrous chloride 10.7

EXAMPLE 6 Nickel chloride l22 Boric acid 32 Sodium bromide 200 Zinc sulphate 0.44

EXAMPLE 7 Nickel chloride l22 Boric acid 32 Sodium bromide 200 Zinc sulphate 0.44 Sodium sulphite 0.5

EXAMPLE 8 Nickel sulphate 144 Boric acid 32 Sodium bromide 200 Cobalt sulphate 42 Sodium sulphite 0.5

EXAMPLE 9 Nickel chloride 122 Boric acid 32 Sodium bromide 200 Nickel phosphite 0.5

EXAMPLE [0 Nickel bromide 145 ing power, an electroformed article free for excessive Boric acid 32 stress and being characterized by great hardness and good Sodium bromide 400 ductility.

2. A method as claimed in claim 1, wherein the pH value of EXAMPLE 1 1 5 the bath is between about l .8 and 5.0.

3. A method as-cla1med1n claim 1, wherein step (3) is cong/l tinued until an electroformed article is obtained which has a minimum thickness of about 0.1 inch. Nickel sulphate I79 4- A method as claimed in claim 1, wherein the bath also Boric acid 32 contains at least one source of metal ions selected from the Sodium bromide 400 group of metals consisting of cobalt, iron, zinc, manganese,

h uranium, molybdenum and vanadium.

TABLE Plating test Hardness, pII Deposit stress Re Ductility Surface 3.6 Present b3 Brittle Matt. 3.6 Slight compresslve Do. 3.5 Present- 49.5 Do.

49 Br ght Do. 68. 6 Matt. 58 Do. 22 Bright 315 Matt. 27 0..-. Do.

lclaim:

l. A method of manufacturing a self-supporting electroformed article by the electrodeposition of a metal selected from the group consisting of nickel and nickel based alloys, 30

comprising 1 providing an electroforming bath of acidic pH and devoid of ammonium ions, which comprises an aqueous solution containing a nickel ion source and at least one water-soluble bromide as a source of bromide ions in which the weight of bromide in the aq the weight of nickel, 2. immersing a substrate in 5. A method as claimed in claim 1, wherein the bath contains a source of sulphite ions.

6. A method as claimed in claim 5, wherein the source of sulphite ions is up to 0.6 g/l of sodium sulphite.

7. A method as claimed in claim 1, wherein step (3) is car ried out in a static bath at a current density below about 50 A.S.F.

8. An electrolytic bath for the production of electroformed nickel articles, comprising an acidic aqueous solution, devoid of ammonium ions, and comprising a source of nickel ions and at least one water-soluble bromide as a source of bromide ions, the weight of bromide being 5 to 20 times the weight of nickel.

9. An electrolytic bath as claimed in claim 8, wherein the pH value of the bath is between about 1.8 to 5.0.

ueous solution is 5 to 20 times the electroforming bath for 

2. A method as claimed in claim 1, wherein the pH value of the bath is between about 1.8 and 5.0.
 2. immersing a substrate in the electroforming bath for receiving the desired electroforming deposit, and
 3. electrolyzing said bath at a current density of up to 100 A.S.F. and at a bath temperature in the range of from 18* to 50* C. to thereby form on the substratE, at high throwing power, an electroformed article free for excessive stress and being characterized by great hardness and good ductility.
 3. A method as claimed in claim 1, wherein step (3) is continued until an electroformed article is obtained which has a minimum thickness of about 0.1 inch.
 4. A method as claimed in claim 1, wherein the bath also contains at least one source of metal ions selected from the group of metals consisting of cobalt, iron, zinc, manganese, uranium, molybdenum and vanadium.
 5. A method as claimed in claim 1, wherein the bath contains a source of sulphite ions.
 6. A method as claimed in claim 5, wherein the source of sulphite ions is up to 0.6 g/l of sodium sulphite.
 7. A method as claimed in claim 1, wherein step (3) is carried out in a static bath at a current density below about 50 A.S.F.
 8. An electrolytic bath for the production of electroformed nickel articles, comprising an acidic aqueous solution, devoid of ammonium ions, and comprising a source of nickel ions and at least one water-soluble bromide as a source of bromide ions, the weight of bromide being 5 to 20 times the weight of nickel.
 9. An electrolytic bath as claimed in claim 8, wherein the pH value of the bath is between about 1.8 to 5.0. 